The present invention relates to a mass spectrometer and a method of mass spectrometry. The preferred embodiment relates to the use or supply of sulphur hexafluoride (“SF6”) as the cone gas to a sampling cone and/or a cone-gas cone of a mass spectrometer.
The efficient transmission of ions from an atmospheric pressure ion source to the vacuum stages of a conventional mass spectrometer is dependent upon a combination of gas flow dynamic effects and the application of electric fields which are maintained throughout the various vacuum stages of the mass spectrometer. Nitrogen gas is commonly used as a carrier gas, or as the background gas, for Atmospheric Pressure Ionization (“API”) ion sources. Nitrogen acts as a cooling/desolvating medium for ions laving a relatively wide range of mass to charge ratios. However, if very high mass ions are desired to be mass analysed then nitrogen has been shown to be a relatively inefficient cooling and/or desolvation gas for such high mass ions over the relatively short ion residence times that ions are typically present in a vacuum stage of a mass spectrometer. Also, ions of very high mass are relatively unsusceptible to the drag due to bulk movement or flow of nitrogen gas molecules and consequently are not effectively drawn or directed by the flow of nitrogen gas.
It is known to attempt to address this problem by increasing significantly the pressure of the nitrogen gas in order to provide more collisions, thereby improving the desolvation and/or cooling of the analyte ions. However, this approach has not been found to be particularly satisfactory for ions with very high masses.
It is therefore desired to provide an improved mass spectrometer.